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HHMI Prokaryotes-T PROKARYOTIC CELLS TEACHER NOTES Alabama Course of Study-Science Biology: 1-Select appropriate laboratory glassware, balances, time measuring equipment, and optical instruments to conduct an experiment. Biology: 4-Describe similarities and differences of cell organelles, using diagrams and tables. Distinguishing between prokaryotic and eukaryotic cells. Biology: 9-Differentiate between the kingdoms. Identifying ways in which organisms from the kingdoms are beneficial and harmful. TIME Prep Time: 15 minutes set up microscopes and distribute prepared bacteria slides. Lab Time: 40 minutes to view, sketch, answer questions, and clean up. GROUP SIZE One or two students per microscope. SAFETY Follow standard laboratory procedures as required when working with microscopes and glass slides. Be sure students are careful if using methylene blue stain not to get it on their skin or clothing. Reassure any concerned students that the bacteria on the prepared slide are dead and preserved and therefore cannot infect them. Preparation Provide lens paper to remove smudges from prepared slides. Make sure adequate number of slides and microscopes are available depending on class size. Secure extension cords if needed. Use plain yogurt. ENGAGE Option 1: Have students compare and contrast prokaryotic and eukaryotic cells. 1. Prokaryotic Cell-Before nucleus 2. Eukaryotic Cell-New nucleus 3. The smaller cell 4. Eukaryotic Cells More than one chromosome Reproduction involves meiosis True nucleus 10-100 micrometers Divides by mitosis Cytoplasmic streaming Membrane-bound organelles Cytoskeleton always present May 2012 Both DNA Plasma membrane Prokaryotic Cells .2-2 micrometers One chromosome Divides by binary fission Page 1 of 4 HHMI Prokaryotes-T After going over the answers, ask students, “how are prokaryotic cells different?” Option 2: Have students view a video such as “Simple Organisms: Bacteria”, “Ebola- The Way of All Flesh”, etc… Option 3: Ask students several questions about bacteria to gain an understanding of their knowledge: 1. What are bacteria? Prokaryotic life form. 2. Where are bacteria located? Bacteria are found throughout the earth in aerobic and anaerobic conditions. 3. Are all bacteria harmful? No, some are decomposers and help break down complex molecules into smaller units for absorption by the intestines or roots of plants (Nitrogen-fixing bacteria). Scientists have discovered that the presence of certain kinds of bacteria is essential for the human body. There are many bacteria that live in the human intestines that contribute to proper digestion. These good bacteria don’t let in bad bacteria and help us digest food that we are unable to process on our own. These bacteria also help to get rid of toxins in our body. Good bacteria improve milk tolerance, regulate digestive function, improve immune response, aid in absorption of nutrients, and decrease food allergies. Many of these helpful bacteria are found in foods such as yogurt, buttermilk, cheese, and vinegar. 4. Can you see a bacterium with the naked eye? No, bacteria are microscopic. However colonies of bacteria (which consist of millions of individual cells) are visible with the naked eye. EXPLORE Part I. Obtain a prepared slide containing the three various shapes on a bacteria smear. Follow proper microscope procedures to sketch each shape on the student worksheet. Label and color each sketch. Answer questions after completing sketches. PartII. Obtain clean slides and cover slips to prepare a thin smear of plain yogurt for microscopic viewing. Add a drop of Methylene blue and water prior to placing the clover slip over the specimen. Follow proper microscope procedures to sketch each shape on the student worksheet. Label and color each sketch. Answer questions after completing sketches. Troubleshooting Check all electrical cords for proper attachment to electrical plugs. Do not use electrical cords that are frayed or damaged. Make sure prepared slides are clean. Make sure the scanning (4X) objective is used to locate the specimen prior to using the low (10x) and high (40x) power objectives. Yogurt at room temperature may give better results. Make sure students do not use too much yogurt on their slide. Make sure students don’t confuse the yogurt clumps for bacteria. May 2012 Page 2 of 4 HHMI Prokaryotes-T Sample Data: Answers to Analysis Questions Part I 1. List three characteristics of prokaryotic cells that distinguish them from eukaryotic cells. No nucleus, Circular ring of DNA, lack membrane bound organelles, smaller than eukaryotic cells, have different cell shapes 2. A. B. C. Name and describe the three common shapes of bacteria. Coccus –round or spherical Bacillus-rod Spirillum-spiral 3. A doctor informs you that you have a Streptococcus pyogenes (Strep Throat) infection. A. Use your knowledge to impress her by drawing a picture what this bacteria would look like below. B. Would the doctor treat this infection with antibiotics? Explain. Yes, this is a bacterial infection and antibiotics can kill bacteria. 4. Why is it necessary to stain bacteria prior to microscopic viewing? The bacteria are transparent and difficult to view prior to staining Part II 1. How many different kinds of bacteria could you find in the yogurt? Answers will vary. Most are cocci and bacilli. Make sure students also note if they were Diplo-, Strepto-, etc. 2. Can you see a nucleus in the bacteria? No nucleus exists and the nucloid is too small to be viewed with the compound microscope. 3. Why is it necessary to stain bacteria prior to microscopic viewing? May 2012 Page 3 of 4 HHMI Prokaryotes-T The stain adheres to the bacteria, making them easier to see. EXPLAIN When most people think of bacteria, they think of disease-causing organisms, like the Streptococcus bacteria, which cause strep throat. While bacteria are notorious for such diseases as tetanus, tuberculosis, and salmonella poisoning, such disease-causing species are a comparatively tiny fraction of the bacteria as a whole. Bacteria are so widespread that it is possible only to make the most general statements about their behaviors and appearances. Bacteria are prokaryotes. They contain a circular ring of DNA. Bacteria lack membrane-bound organelles. Most bacteria are colorless. This feature makes them difficult to view under a microscope. They may be found on the tops of the highest mountains, the bottoms of the deepest oceans, in the guts of animals, and even on the frozen rocks and ice of Antarctica. One feature that has enabled them to spread so far, and last so long is their ability to go dormant for extended periods of time. When conditions are good they come out of dormancy to grow and reproduce. Most bacteria are considered decomposers and help break down complex molecules into smaller units. This same process occurs in the intestines of animals and the roots of some plants (e.g. nitrogen fixing bacteria). There are many bacteria that live in the human intestines that contribute to proper digestion. Scientists have discovered that the presence of certain bacteria is essential for the human body. These good bacteria out compete bad bacteria under normal conditions and help us digest food that we are unable to process on our own. These bacteria also help to get rid of toxins in our body. Good bacteria improve milk tolerance, regulate digestive function, improve immune response, aid in absorption of nutrients, and decrease food allergies. Many of these helpful bacteria are found in foods such as yogurt, buttermilk, cheese, and vinegar. EVALUATE Students should be graded on microscope use, sketches, and answers to questions. EXTEND 1. Complete the “Antibiotic Resistance” activity. 2. Discuss Gram staining. Review slides to determine which bacteria are Gram positive and which are Gram negative. 3. Make yogurt. May 2012 Page 4 of 4